The subject matter disclosed herein relates to elevator systems. More specifically, the subject disclosure relates to tension members for elevator suspension and/or driving.
Elevator systems utilize a lifting means, such as ropes or belts operably connected to an elevator car, and routed over one or more sheaves, also known as pulleys, to propel the elevator along a hoistway. Lifting belts in particular typically include a plurality of wires at least partially within a jacket material. The plurality of wires are often arranged into one or more strands and the strands are then arranged into one or more cords.
Wire arrangements are typically designed with at least three basic requirements in mind, breaking strength, cord life, and torque or twist. The total cross-sectional area of steel used in the cord is the primary determinant of breaking strength of the cord. A large number of small cross-section wires are typically avoided for cost and manufacturing reasons and large cross-section wires would be expected to have a limited fatigue life thus limiting the overall life of the cord. Further, nearly equal wire cross-sectional areas are typically preferred, since the largest wire usually has the shortest fatigue life and becomes the limiting element when determining cord life.
In a lifting belt construction, a plurality of cords are typically arranged equally spaced within a jacket in a longitudinal direction, the cords having alternating S and Z lay directions. To maintain belts that lack guidance features (e.g. ribs or poly-V configurations) centered on sheaves of the elevator system, the sheaves include a convex crown feature. Incorporation of such a crown on the sheaves influences mechanical and fatigue behavior of the cords, for example those cords furthest from the peak of the crown are most lightly loaded.